Experiments have been performed testing the ability of transplanted liver or bone marrow cells to provide enzyme replacement therapy in animal models of congenital enzyme deficiency diseases or for liver cells to provide metabolic support for experimental acute liver failure. Bone marrow from normal catalasemic mice donors transplanted to sublethally irradiated congeneic acatalasemic mice restores blood but not liver catalase to normal. Hepatocyte transplantation has a normal effect on liver and no effect on blood catalase. Transplantation of liver cells from normal to UDPGT deficient Gunn rats results in decreased bilirubin levels in some recipients, but technical and immunologic problems remain to be solved. Transplantation of autologous, syngeneic and allogeneic hepatocytes can improve the survival in rats with chemically acute liver failure, and a dog model of ischemic liver failure has shown that intrasplenic transplants of autologous hepatocytes prepared from a normal lobe of the dog liver can also improve survival by providing metabolic support during a critical period necessary for recovery. Experiments in progress are designed to improve the techniques of metabolic support by cellular transplantation and to circumvent the immunological problem associated with adapting the techniques for allotransplantation.